Home made lapping plate - 2 vs 3 plates

[compact8]

Another significant point is that after the two plates are charged with abrasive, they could not be used in contact with the surface plate without causing wear and inaccuracy to it.

Yes. I didn't know anything about embedding until I learned it the hard way. When I first tried lapping I used diamond to lap a steel plate and after finishing it and cleaning it all over, I put the plate on the table of my mill and slided it across. The result is shown in the photo below . That's why I have switched to garnet which is said to be non-embedding.

 

[compact8]

what level of precision do you need?

I will be happy if I can get an evenly colored surface after rubbing against my dyed granite surface plate. This is achievable in practice even by a novice like me although I am not sure if I can get the wanted result consistently. The following pictures show what I have seen so far.

 

[Dan Krager]

I know nothing about this process. But inquiring minds want to know.

What causes the curvature to develop?

And if you reversed the plates to get a flat surface, how would you know when to stop?

What assures uniformity across the surface, flat or not?

DanK

 

[gradient]

Look at about 14 minutes in on the second part of the video that DavidR8 presents. There is a brief mention there of why you need 3 flat surfaces. Basically, when you use only 2 plates you swap the imperfections back and forth perfectly. Both plates will eventually match each other but are not necessarily flat. The third plate forces the common fit to be flat.